JP2011227340A - Liquid crystal display device and control program thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately carry out control for flicker reduction.SOLUTION: A liquid crystal display device 1 includes: a liquid crystal display element 50 which displays picture images by modulating light; driving means 74 which drives the liquid crystal display element in response to input image signals; flicker detecting means 80 which detects flicker generated by the liquid crystal display element; driving condition setting means 73 which sets, in accordance with flicker detection results from the flicker detecting means, driving conditions under which the driving means drives the liquid crystal display element to a specific driving condition for reducing flicker; an input picture image detecting means 71 which detects information on the gradation of input image signals; and selecting means 72 which carries out, in accordance with the information on the gradation, one of the following: determining whether or not the liquid crystal display element is driven under the specific driving condition; determining whether or not flicker is detected using the flicker detecting means; and changing the setting method of the specific driving condition by the driving condition setting means.

Description

  The present invention relates to a display device using a liquid crystal display element such as a liquid crystal projector or a liquid crystal monitor.

The liquid crystal display element uses the ECB (Electrically Controlled Birefringence) effect to form an image by controlling the action (modulation) of changing the polarization state of the light wave by providing retardation to the light wave passing through the liquid crystal layer. There is something to do.

  As a driving method of such a liquid crystal display element, there is an inversion driving method in which the positive / negative polarity of a voltage applied to each line of the array pixels or all (fields) of the array pixels is inverted at a specific frequency. According to the inversion drive method, the voltage applied to the liquid crystal layer can be prevented from having a certain polarity, and an unnecessary voltage is generated due to the uneven distribution of ionic substances in the liquid crystal layer, thereby driving the liquid crystal layer appropriately. It is possible to avoid a change in voltage (effective voltage) that should be substantially applied to the liquid crystal layer.

  However, the change in effective voltage is not only due to the uneven distribution of ionic substances, but may be due to other factors. For example, charges of electrons and holes themselves may be trapped in an insulating non-conductive film (a liquid crystal alignment film, a reflection enhancement film, an inorganic passivation film for preventing metal elution, etc.). If electrons or holes are trapped, the interface of the film causes charge-up, and the effective voltage to the liquid crystal layer may change due to this electrostatic charging.

  When electrostatic charging has occurred in this way, when the liquid crystal display element is driven by the above-described inversion driving method, the absolute value of the positive potential difference (voltage) and the absolute value of the negative potential difference (voltage) are reduced. The difference increases. As a result, the brightness when a positive potential difference is applied and the brightness when a negative potential difference are applied are different from each other, and this is called flicker in which bright and dark images are alternately displayed at an inverted drive frequency. Occurs. This flicker is said to be visible to the human eye when the difference between the absolute value of the positive potential difference and the absolute value of the negative potential difference is 200 mV or more in the general field inversion drive method that inverts at 120 Hz.

  For example, in the liquid crystal display device disclosed in Patent Document 1, the luminance of the modulated light is detected by a luminance sensor arranged on the optical path of the modulated light that does not enter the projection optical system, and the maximum and minimum values of the detected luminance are detected. Is obtained as a flicker value. Then, the voltage applied to the common electrode is changed according to the flicker value, and the voltage corresponding to the minimum flicker value is set.

  Further, in the liquid crystal display device disclosed in Patent Document 2, a plurality of luminance sensors that detect the luminance of the color-combined image light for each wavelength range are arranged between the color synthesis prism and the projection optical system. Yes. Based on the output of the luminance sensor, the voltage of the common electrode is adjusted so that the flicker is minimized.

Japanese Patent Laid-Open No. 2005-22169 JP 2008-26613 A

In the liquid crystal display devices disclosed in Patent Documents 1 and 2, flicker is minimized when an image suitable for detecting flicker is displayed, for example, an image having an intermediate gradation as a whole. It is possible to determine the common electrode voltage. However, liquid crystal display devices often display general presentation images and moving images, and when these images are displayed, it is difficult to accurately detect flicker. In such a case, there is a possibility that the common electrode voltage that minimizes flicker is set inappropriately.

  The present invention provides a liquid crystal display device capable of appropriately performing control for reducing flicker.

  A liquid crystal display device according to an aspect of the present invention includes a liquid crystal display element that modulates light to display an image, a driving unit that drives the liquid crystal display element in accordance with an input image signal, and flicker generated in the liquid crystal display element. A flicker detection means for detecting the flicker, a drive condition setting means for setting the drive condition of the liquid crystal display element by the drive means to a specific drive condition for reducing flicker according to the flicker detection result by the flicker detection means, and an input Input image detection means for detecting information relating to the gradation of the image signal, selection of whether or not to drive the liquid crystal display element according to a specific drive condition, and detection of flicker by the flicker detection means in accordance with the information relating to the gradation Selection means for performing any one of selection of whether or not to perform and change of a setting method of the specific drive condition by the drive condition setting means.

  A control program according to another aspect of the present invention includes a liquid crystal display element that modulates light to display an image, a driving unit that drives the liquid crystal display element in accordance with an input image signal, and a liquid crystal display element. A liquid crystal display device having flicker detection means for detecting generated flicker is controlled. The control program sets a driving condition of the liquid crystal display element by the driving means to a specific driving condition for reducing flicker according to a flicker detection result by the flicker detecting means, Step for detecting information relating to gradation, selection of whether or not to drive the liquid crystal display element according to a specific driving condition, and selection of whether or not to perform flicker detection by the flicker detection means according to the information relating to the gradation And a step of performing any one of the change of the setting method of the specific driving condition by the driving condition setting means.

According to the present invention, control for reducing flicker can be appropriately performed in a liquid crystal display device, and control for reducing flicker is inappropriately performed depending on the type of image to be displayed as in the past. The problem can be solved.

1 is a diagram illustrating a configuration of a control unit in a liquid crystal display device that is Embodiment 1 of the present invention. FIG. 1 is a diagram illustrating a configuration of a liquid crystal display device according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view illustrating a structure of a liquid crystal display element used in the liquid crystal display device of Example 1. FIG. 3 is a diagram illustrating changes in effective voltage applied to the liquid crystal display element and luminance of the liquid crystal display element in a state where flicker is not generated in the first embodiment. FIG. 6 is a diagram illustrating changes in effective voltage applied to the liquid crystal display element and luminance of the liquid crystal display element in a state where flicker is generated in the first embodiment. FIG. 3 is a diagram illustrating an arrangement example of flicker detectors according to the first embodiment. 5 is a flowchart illustrating flicker suppression processing according to the first embodiment. FIG. 6 is a diagram illustrating an image in which flicker is difficult to detect in Example 1, a histogram thereof, and luminance of a liquid crystal display element. FIG. 3 is a diagram illustrating an image in which flicker is easily detected in Example 1, a histogram thereof, and luminance of a liquid crystal display element. FIG. 3 is a graph showing voltage-gradation characteristics of a liquid crystal display element in Example 1. 3 is a diagram illustrating a correlation between a common electrode voltage applied to a liquid crystal display element and a flicker amount in Embodiment 1. FIG. 9 is a flowchart showing flicker suppression processing in a liquid crystal display device that is Embodiment 2 of the present invention. 9 is a flowchart showing flicker suppression processing in a liquid crystal display device that is Embodiment 4 of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a configuration of a liquid crystal projector (image projection apparatus) 1 as a liquid crystal display apparatus that is Embodiment 1 of the present invention.

  The liquid crystal projector 1 includes a housing 1a, a light source lamp 10, an illumination optical system 20, a color separation / synthesis optical system 30, a projection lens (projection optical system) 40, and reflective liquid crystal display elements 50R, 50G, and 50B. And an enlarged image of the original image displayed on each reflective liquid crystal display element is projected onto the screen 200. The liquid crystal projector 1 also includes a storage unit 60 that stores various data and computer programs, and a control unit 70 that controls driving of the reflective liquid crystal display elements 50R, 50G, and 50B.

  The housing 1a stores and holds the parts and members constituting the liquid crystal projector 1.

  The light source lamp 10 includes a discharge arc tube 11 and a reflector 12, and the arc tube 11 emits white light having a continuous spectrum. The reflector 12 emits the light emitted from the arc tube 11 toward the illumination optical system 20.

  The illumination optical system 20 transmits the light from the light source lamp 10 to the color separation / synthesis optical system 30. The illumination optical system 20 includes cylinder lens arrays (lens arrays) 21 and 22, an ultraviolet absorption filter 23, a polarization conversion element 24, a front compressor (lens) 25, a reflection mirror 26, a condenser lens 27, and a rear compressor. (Lens) 28.

  The light flux from the light source lamp 10 is divided into a plurality of light fluxes by the cylinder lens arrays 21 and 22, and further adjusted to a light flux shape suitable for illuminating each reflective liquid crystal display element by the front compressor 25 and the rear compressor 28. The plurality of light beams are superimposed on each reflective liquid crystal display element by the condenser lens 27. The polarization conversion element 24 converts non-polarized light from the light source lamp 10 into S-polarized light. The ultraviolet absorption filter 23 absorbs ultraviolet rays contained in the light from the light source lamp 10. The reflection mirror 26 bends the optical path of light from the light source lamp 10 by 90 °.

  The color separation / combination optical system 30 decomposes white light from the light source lamp 10 into three color lights of R (red), G (green), and B (blue), and three reflective liquid crystal display elements 50R, 50G, and 50B. Lead to. Further, the color separation / synthesis optical system 30 combines the three color lights modulated according to the original image by the reflective liquid crystal display elements 50R, 50G, and 50B and guides them to the projection lens 40. The color separation / synthesis optical system 30 includes a dichroic mirror 31, polarizing plates 32a, 32b, and 32c, polarizing beam splitters 33a, 33b, and 33c, quarter-wave plates 35R, 35G, and 35B, and a color-selective retardation plate. 36a, 36b.

  The dichroic mirror 31 transmits G light and reflects light in the wavelength region of B light and R light. The G light as S-polarized light transmitted through the dichroic mirror 31 passes through the polarizing plate 32a, is reflected by the polarizing beam splitter 33a, and is guided to the G reflective liquid crystal display element 50G through the quarter-wave plate 35G. .

  The liquid crystal projector 1 receives an image signal (input image signal or input image) supplied from an image supply device (not shown) such as a personal computer, a DVD player, or a TV tuner. The liquid crystal projector 1 and the image supply device constitute an image display system.

  The control unit 70 drives the reflective liquid crystal display elements 50R, 50G, and 50B according to the input image signal. Thereby, the R original image, the G original image, and the B original image corresponding to the image signal are respectively displayed on the liquid crystal display elements 50R, 50G, and 50B, and the light incident on each liquid crystal display element is image-modulated and reflected. .

  The G light modulated and reflected by the reflective liquid crystal display element 50G displaying the G original image is again converted to P-polarized light through the quarter-wave plate 35G, and transmitted through the polarization beam splitter 33a to be polarized. The light enters the beam splitter 33c.

  Of the B light and R light reflected by the dichroic mirror 31 and passing through the polarizing plate 32b, the R light that is S-polarized light that has passed through the color-selective retardation plate 36a passes through the polarizing plate 32b and passes through the polarizing beam splitter 33b. It is reflected by. Then, the R light is guided to the reflective liquid crystal display element 50R for R through the quarter wavelength plate 35R. The R light modulated and reflected by the reflective liquid crystal display element 50R displaying the R original image is again converted into P-polarized light through the quarter-wave plate 35R and transmitted through the polarization beam splitter 33b. The R light is converted to S-polarized light by the color selective phase difference plate 36b, analyzed by the polarizing plate 32c, and then incident on the polarizing beam splitter 33c.

  The B light that has passed through the polarizing plate 32b and has been converted to P-polarized light by the color-selective retardation plate 36a passes through the polarizing beam splitter 33b, passes through the quarter-wave plate 35B, and is a B-type reflective liquid crystal display element. Guided to 50B. The B light modulated and reflected by the reflective liquid crystal display element 50B displaying the B original image is again converted to S-polarized light through the quarter-wave plate 35B and reflected by the polarization beam splitter 33b. The B light passes through the color selective retardation plate 36b as it is, is analyzed by the polarizing plate 32c, and then enters the polarizing beam splitter 33c.

  The G light as P-polarized light incident on the polarization beam splitter 33c passes through the polarization beam splitter 33c and travels toward the projection lens 40. Further, the R light and B light as S-polarized light incident on the polarization beam splitter 33c are reflected by the polarization beam splitter 33c and travel toward the projection lens 40.

  The combined R light, G light, and B light are enlarged and projected onto the screen 200 by the projection lens 40, and a color image corresponding to the R, G, and B original images is displayed on the screen 200.

  FIG. 3 shows the structure of the reflective liquid crystal display element 50 (50R, 50G, 50B). The liquid crystal display element 50 is configured by disposing a liquid crystal material (liquid crystal layer) 55 between a counter substrate (transmission substrate) 51 and a drive substrate 56.

  The counter substrate 51 includes a glass substrate 52, a transparent electrode (common electrode) 53 formed on the surface of the glass substrate 52 on the liquid crystal layer side, and an alignment film disposed between the transparent electrode 53 and the liquid crystal layer 55. 54. The glass substrate 52 transmits light incident from the light source side. The transparent electrode 53 applies an electric field to the liquid crystal molecules of the liquid crystal layer 55 by passing a current therethrough. The transparent electrode 53 is a thin film of indium tin oxide (ITO). The alignment film 54 is formed by obliquely depositing an inorganic material such as SiO on the surface of the transparent electrode 53, has an inclined columnar structure, and directs liquid crystal molecules in a certain direction.

  The direction of the liquid crystal molecules changes according to the electric field applied to the liquid crystal layer 55. By changing the electric field according to the image signal, an image corresponding to the image signal (original image in the liquid crystal projector 1) is formed on the liquid crystal layer 55.

  The liquid crystal material is in an intermediate state between a liquid and a solid, and there are types such as a cholesteric liquid crystal, a smectic liquid crystal, and a nematic liquid crystal. In this embodiment, any of these liquid crystal materials may be used.

  The drive substrate 56 includes an alignment film 57, a pixel electrode 58, and a Si substrate 59. The alignment film 57 is formed on the surface of the Si substrate 59 in the same manner as the alignment film 54 described above, and directs liquid crystal molecules in a certain direction. The pixel electrode 58 is a plurality of electrodes provided on the Si substrate 59, and applies an electric field for each pixel to the liquid crystal layer 55 disposed between the transparent electrode 53. By controlling the electric field for each pixel, an image can be formed on the liquid crystal layer 55 as described above.

  The Si substrate 59 is formed of silicon (Si), and a mirror (not shown) is formed on the surface on the liquid crystal layer side. Instead of the Si substrate 59, a light-shielding substrate such as a plastic substrate can be used.

  The driving of the liquid crystal display element 50 when performing image display will be described. In the liquid crystal projector of this embodiment, it is possible to change the image to be displayed every 1/60 second period (one frame). In this case, based on the same image signal (input image signal or input image) input every 1/60 seconds, the control unit 70 is a voltage (effective voltage or effective electric field) having the same magnitude but different positive and negative polarities. Is applied to the liquid crystal layer 55 through the drive substrate 56 at a 1/120 second period (one field). That is, based on one frame image with a period of 1/60 seconds, first, a positive voltage is applied to the liquid crystal layer 55 for 1/120 seconds to display a one-field image, and for 1/120 seconds thereafter. A negative voltage of the same magnitude is applied to the liquid crystal layer 55 to display a one-field image.

  In such field inversion driving of the liquid crystal display element 50, when the difference between the positive and negative effective voltages (absolute values) that should be the same size exceeds a certain value, the liquid crystal display element 50 generates each field. Flicker, which is a change in brightness, increases and becomes visible to the human eye.

  In this embodiment, the case where the field inversion driving is performed as described above will be described. However, the driving is performed so as to invert the positive / negative polarity of the voltage applied to the liquid crystal layer 55 every frame (every 1/60 seconds). It doesn't matter. However, in this case, since the cycle of the luminance change is longer than in the field inversion driving, flicker becomes more conspicuous.

  In this embodiment, the positive and negative effective voltages applied to the liquid crystal layer 55, that is, the difference between the positive and negative effective voltages actually applied to the liquid crystal layer 55 is the same in the state where the same image is continuously displayed. Is the difference between the absolute values of the voltages. Further, in the present embodiment, “flicker” includes not only a thing that can be seen by human eyes but also a small luminance change that cannot be seen by human eyes.

  The principle of occurrence of flicker will be described with reference to FIGS. FIG. 4A is a graph showing the time change of the effective voltage applied to the liquid crystal layer 55 in a state where flicker is not generated, and FIG. 4B is a graph showing the time change of the luminance corresponding thereto. It is. FIG. 5A is a graph showing a time change of the effective voltage applied to the liquid crystal layer 55 in a state where flicker is generated, and FIG. 5B is a graph showing a time change of the luminance corresponding thereto. is there.

  The potential (or voltage) at the end of the liquid crystal layer 55 on the common electrode 53 side is α, and the potential (or voltage) at the end of the liquid crystal layer 55 on the pixel electrode 58 side is β. The potential β may be a positive value or a negative value relative to the potential α. The potential difference (β−α) applied to the liquid crystal layer 55 when the potential β is a positive value and the potential difference (α−β) applied to the liquid crystal layer 55 when the potential β is a negative value. If they are equal to each other, no flicker occurs.

  However, the effective voltage (effective electric field) applied to the liquid crystal layer 55 and the voltage applied between the electrodes 53 and 58 may differ from each other due to various charging phenomena in the liquid crystal display element 50. That is, the potential of the common electrode 53 and the potential at the end of the liquid crystal layer 55 on the common electrode side are different from each other, or the potential of the pixel electrode 58 and the potential at the end of the liquid crystal layer 55 on the pixel electrode side are different from each other. Sometimes. Furthermore, the common electrode 53, the pixel electrode 58, and other constituent members of the liquid crystal display element 50 may be charged. Such a charging phenomenon occurs remarkably in a liquid crystal projector in which the intensity of light applied to the liquid crystal display element 50 is high. The charging phenomenon here is a general term for movement of ionic substances in the liquid crystal display element 50, charging phenomenon of components, and the like.

  In the state where the positive and negative effective voltages (α, β) applied to the liquid crystal layer 55 are equal to each other as shown in FIG. 4A, when the positive effective voltage is applied as shown in FIG. There is no change in the brightness of the image displayed on the liquid crystal display element 50 when the negative effective voltage is applied. For this reason, no flicker occurs.

  When the positive and negative effective voltages are different from each other as shown in FIG. 5A (there is a difference α ′) and the asymmetry of the effective voltage occurs, the positive effective voltage as shown in FIG. The brightness of the image displayed on the liquid crystal display element 50 varies between when the voltage is applied and when the negative effective voltage is applied. For this reason, flicker occurs.

  Further, the movement of the ionic substance in the liquid crystal display element 50 and the charging at the film at the substrate interface are not uniform over the entire display area of the liquid crystal display element 50. Therefore, the potential of the common electrode 53 for suppressing (decreasing) flicker differs for each area in the liquid crystal display element 50.

  In the conventional liquid crystal display device, the positive effective voltage and the negative effective voltage applied to the liquid crystal layer 55 are adjusted to be equal to each other at the time of shipment from the factory in order to prevent the occurrence of flicker. That is, by adjusting the potential of the common electrode 53 and the potential of the pixel electrode 58, the driving conditions are adjusted so as to suppress the occurrence of flicker.

  However, even if such adjustment is performed, if the usage time by the user becomes longer, the asymmetry of the effective voltage occurs due to the uneven distribution of ionic substances and the accumulation of charged charges in the liquid crystal display element 50, and flicker. Will occur.

  In this embodiment, in order to suppress the occurrence of such flicker, the control unit 70 is configured as shown in FIG. 1 and a flicker detector 80 is provided. The control unit 70 includes a drive unit 74 as a drive unit, a flicker suppressing unit 73 as a drive condition setting unit, an input image detection unit 71 as an input image detection unit, and a control selection unit 72 as a selection unit. .

  The input image signal (Vsig) from the above-described image supply device is converted into a drive signal (Lcsig) suitable for driving the liquid crystal display element 50 by the drive unit 74 in the control unit 70 and output to the liquid crystal display element 50. The The drive signal (Lcsig) includes a signal voltage applied to the pixel electrode 58 of the liquid crystal display element 50, a common electrode voltage (Vcom) applied to the common electrode 53, and the like.

  The flicker detector 80 is an optical sensor for detecting light modulated by the liquid crystal display element 50, a filter for removing noise components from the output of the optical sensor, and an output that has passed through the filter as a digital signal. And an A / D converter for converting into Further, the flicker detector 80 also has a calculation unit that reads the amplitude of the digital signal from the A / D converter.

  The flicker suppressing unit 73 changes the common electrode voltage (Vcom) in the drive signal (Lcsig), and detects the output amplitude of the flicker detector 80 at that time as the flicker amount (LVflk). That is, flicker generated in the image display element 50 is detected by the flicker detector 80 and the flicker suppressing unit 73.

  As shown in FIG. 6, the optical sensor of the flicker detector 80 is disposed beside (near) the polarizing beam splitter 33c. By disposing the flicker detector 80 at this position, it is possible to detect the light (that is, flicker) modulated by the liquid crystal display element 50 without blocking the light (projected image) toward the projection lens 40.

  Three flicker detectors 80 may be provided so as to correspond to the three liquid crystal display elements 50R, 50G, and 50B shown in FIG. In this case, the optical sensor of each flicker detector 80 is preferably provided with a filter that transmits only the color light to be detected so that only the color light to be detected can be detected. Further, the flicker detector 80 is provided only for one of the three liquid crystal display elements 50R, 50G, and 50B (for example, the G liquid crystal display element 50G that is most sensitive to human visual characteristics). Also good.

  The flowchart of FIG. 7 shows the flow of flicker suppression processing (control method) performed by the control unit 70 of the present embodiment. Hereinafter, the functions of the flicker suppressing unit 73, the input image detecting unit 71, and the control selecting unit 72 will be described together with the flicker suppressing process. Further, the flicker suppression process is executed in accordance with a computer program (control program) stored in a memory (not shown) in the control unit 70.

  First, in the control unit 70, the input image detection unit 71 captures an input image signal (Vsig). The input image detection unit 71 detects a gradation distribution as information regarding the gradation of one frame in the input image signal, and creates a histogram representing the gradation distribution (Step 1). Then, the input image detection unit 71 transfers the created histogram to the control selection unit 72 (Step 2).

  The control selection unit 72 analyzes the histogram (Step 3), and the input image (that is, the image displayed on the image display element 50) is an image suitable for detecting flicker through the flicker detection unit 80 (hereinafter referred to as flicker). It is determined whether or not it is called a detectable image (Step 4). Specifically, in this embodiment, the image is represented by a representative value of gradation when specific weighting is applied to the gradation distribution represented by the histogram, for example, a mode value (a value with the highest Count). It is determined whether the image is flicker detectable.

  For example, FIG. 8A shows a material image used in a presentation or the like in a general meeting, and FIG. 8B shows a histogram of the material image. FIG. 8C shows a light detection waveform by the flicker detector 80 when the material image is displayed on the liquid crystal display element 50. FIG. 9A shows a natural image such as a photograph, and FIG. 9B shows a histogram of the natural image. FIG. 9C shows a light detection waveform by the flicker detector 80 when the natural image is displayed on the liquid crystal display element 50.

  A document image as shown in FIG. 8A is often an image with a high contrast and a clear contrast as shown in FIG. 8B. When such a document image is displayed on the liquid crystal display element 50, the light detection waveform by the flicker detection unit 80 is substantially flat as shown in FIG. 8C, and flicker cannot be detected with high accuracy.

  On the other hand, in the case of a natural image as shown in FIG. 9A, as shown in FIG. When such a natural image is displayed on the liquid crystal display element 50, the light detection waveform by the flicker detection unit 80 has a large change as shown in FIG. 9C, and flicker can be detected with high accuracy. .

  This can be explained from the characteristics of the liquid crystal display element 50. When displaying a bright (high) gradation or a dark (low) gradation on the liquid crystal display element 50, the voltage applied to the liquid crystal display element 50 (liquid crystal layer 55) is increased or decreased. FIG. 10 shows the voltage-display gradation characteristics of the liquid crystal display element 50 in which the display gradation becomes brighter as the applied voltage is higher.

  As a general electro-optical characteristic of the liquid crystal display element 50, in a certain applied voltage range M, a change in display gradation with respect to a change in applied voltage is large, but in an applied voltage range H higher and lower than that range, The change in display gradation with respect to the change in applied voltage is small. Therefore, flicker generated due to the asymmetry of the effective voltage applied to the liquid crystal display element 50 is difficult to detect with high accuracy unless the change in the display gradation with respect to the change in the applied voltage is large.

  Therefore, as a result of analyzing the histogram, the control selection unit 72 determines that an image having a high frequency (Count) of at least one of the low gradation side and the high gradation side is not a flicker detectable image. In this case, the control selection unit 72 causes the flicker suppression unit 73 to drive the liquid crystal display element 50 for suppressing the occurrence of flicker (reducing flicker) (specific drive condition: hereinafter referred to as flicker suppression drive condition). ) Is not set (Step 9). Receiving this instruction, the flicker suppression unit 73 detects the amount of flicker through the flicker detector 80, but does not set the flicker suppression drive condition according to the detection result.

  On the other hand, as a result of analyzing the histogram, the control selection unit 72 determines that an image having a low frequency on both the low gradation side and the high gradation side and a high intermediate gradation frequency is a flicker detectable image. In this case, the control selection unit 72 detects the flicker amount through the flicker detector 80 with respect to the flicker suppression unit 73 and sets the flicker suppression driving condition of the liquid crystal display element 50 according to the detection result. A suppression instruction is issued (Step 5). As described above, the control selection unit 72 selects whether to set the flicker suppression driving condition of the liquid crystal display element 50 according to the histogram of the input image.

  In response to the flicker suppression instruction, the flicker suppression unit 73 performs the common electrode voltage until the flicker amount (LVflk) detected through the flicker detector 80 reaches the minimum level (minimum value or a value close thereto) as shown in FIG. (Vcom) is changed (Steps 5, 6, and 7). The amount of change in the common electrode voltage at this time is preferably set in a range in which the brightness and color of the projected image viewed by the user do not change.

  Then, the common electrode voltage (Vcom) when the flicker amount (LVflk) reaches the minimum level is set as a flicker suppression drive condition through the drive unit 74 (Step 8). In this way, flicker suppression driving conditions are detected (or selected) and set, and the occurrence of flicker in the liquid crystal display element 50 is suppressed.

  According to the present embodiment, it is possible to detect flicker with high accuracy while displaying a normal viewing image as shown in FIG. 9A as a flicker detectable image instead of an image dedicated to flicker detection. The drive condition of the liquid crystal display element 50 for suppression can be set (changed). In addition, the driving conditions of the liquid crystal display element 50 for flicker detection and flicker suppression are not set in a state where an image unsuitable for flicker detection as shown in FIG. 8A is displayed. For this reason, it is possible to avoid setting an inappropriate driving condition based on erroneous flicker detection.

  In this embodiment, the case where the common electrode voltage is set as the driving condition for suppressing the occurrence of flicker has been described. However, the voltage applied to the pixel electrode may be used as the driving condition.

  Next, a liquid crystal projector according to a second embodiment of the present invention will be described. In the liquid crystal projector of the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

  In the first embodiment, the case where the flicker suppression driving condition of the liquid crystal display element 50 is not set when it is determined that the input image is not a flicker detectable image has been described. However, when it is determined that the input image is not a flicker-detectable image, the flicker suppression driving condition setting method may be changed to improve the flicker detection accuracy and the flicker suppression driving condition setting accuracy.

  As can be seen from the voltage-gradation characteristics of the liquid crystal display element 50 shown in FIG. 10, in the applied voltage range M where the change in the display gradation with respect to the change in the applied voltage to the liquid crystal layer 55 is large, the change in the common electrode voltage. The change in flicker amount is also large. On the other hand, in the applied voltage ranges L and H in which the change in display gradation with respect to the change in the applied voltage to the liquid crystal layer 55 is small, the change in the flicker amount with respect to the change in the common electrode voltage is also small.

  When it is determined from the histogram of the input image that the gradation of the applied voltage range M is dominant (a flicker-detectable image), the control selection unit 72 selects a flicker suppression driving condition by the flicker suppression unit 73. The amount of change of the common electrode voltage at one time is set to ΔVcomm. ΔVcomm is set in a range in which the brightness and color of the projected image viewed by the user do not change. Then, as shown in FIG. 11, a common electrode voltage (flicker suppression driving condition) at which the flicker amount (LVflk) becomes the minimum level is obtained.

  On the other hand, when it is determined from the histogram that the gradations of the applied voltage ranges L and H are dominant (not flicker-detectable images), the control selection unit 72 selects the common electrode voltage when selecting the flicker suppression driving condition. Is set to ΔVcomL or ΔVcomH. Here, ΔVcomL> ΔVcomm and ΔVcomH> ΔVcomm. Then, the common electrode voltage (flicker suppression drive voltage) at which the flicker amount (LVflk) becomes the minimum level is obtained.

  As described above, in the present embodiment, the flicker suppression driving condition setting method (in other words, the detection method or the selection method) is changed according to the histogram of the input image.

  The flowchart of FIG. 12 shows the flow of flicker suppression processing (control method) performed by the control unit 70 of this embodiment. The flicker suppression process is executed according to a computer program (control program) stored in a memory (not shown) in the control unit 70. In the flowchart of FIG. 12, a single change amount of the common electrode voltage when the control selection unit 72 determines that the gradations of the applied voltage ranges L and H are dominant is described as ΔVcomH.

  Step 1 to Step 3 are the same as Step 1 to Step 3 of FIG. 7 described in the first embodiment.

  The control selection unit 72 that has analyzed the histogram at Step 3 determines whether or not the input image is an image with a high frequency of intermediate gradation (applied voltage range M) (Step 11). If it is determined that the image has a high halftone frequency, the control selection unit 72 instructs the flicker suppression unit 73 to perform the flicker suppression driving condition of the liquid crystal display element 50 according to the detection result of the flicker amount through the flicker detector 80. A flicker suppression instruction is issued so as to set (Step 5).

  In response to the flicker suppression instruction, the flicker suppression unit 73 changes the common electrode voltage until the flicker amount detected through the flicker detector 80 reaches the minimum level (Steps 5, 6, and 7). The amount of change of the common electrode voltage at this time is ΔVcomm. Then, the common electrode voltage when the flicker amount reaches the minimum level is set as a flicker suppression driving condition through the driving unit 74 (Step 8). Thereby, generation | occurrence | production of the flicker in the liquid crystal display element 50 is suppressed.

  On the other hand, also when it is determined in Step 11 that the frequency of the intermediate gradation of the input image is low, the control selection unit 72 issues a flicker suppression instruction to the flicker suppression unit 73 (Step 12). In response to the flicker suppression instruction, the flicker suppression unit 73 changes the common electrode voltage until the flicker amount detected through the flicker detector 80 reaches the minimum level (Steps 12, 13, and 14). However, the amount of change of the common electrode voltage at this time is ΔVcomH, and the setting method of the flicker suppression driving condition is different from the case of proceeding from Step 6 to Step 8.

  Then, the common electrode voltage when the flicker amount reaches the minimum level is set as a flicker suppression driving condition through the driving unit 74 (Step 8). Thereby, generation | occurrence | production of the flicker in the liquid crystal display element 50 is suppressed.

  As described above, in the applied voltage range M in which flicker is likely to occur even if the asymmetry of the effective voltage applied to the liquid crystal layer is small, the amount of change (ΔVcomm) of the common electrode voltage is reduced to make the flicker stand out. The flicker suppression driving condition is set with high accuracy without causing the flicker. On the other hand, in the applied voltage ranges L and H in which flicker is unlikely to occur when the asymmetry of the effective voltage is small, the amount of change (ΔVcomL, ΔVcomH) of the common electrode voltage is increased to detect flicker with high accuracy. Set suppression drive conditions with high accuracy.

  Next, a liquid crystal projector according to a third embodiment of the present invention will be described. In the liquid crystal projector of the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

  In the first embodiment, the case has been described where it is determined whether or not the input image is a flicker-detectable image based on the mode value when specific weighting is performed on the gradation of the histogram of the input image. However, whether or not the input image is a flicker-detectable image based on the amount of time change of the histogram of the input image and the mode value when specific weighting is performed on the average value of the gradation per unit time of the histogram of the input image. It may be judged.

  When a still image is input from the image supply device, the histogram obtained by the input image detection unit 71 is substantially constant until the still image is switched. Therefore, if the input image is a still image, the amount of time change in the histogram of the input image is almost zero, and the average gradation value per unit time of the histogram corresponds to the gradation of the still image that is currently input. To do. Then, according to the mode value when specific weighting is performed on the gradation of the histogram, it is determined in the same manner as in the first embodiment whether or not the inputted still image is a flicker detectable image. Can do.

  On the other hand, when a moving image is input from the image supply device, the histogram obtained by the input image detection unit 71 changes with time. When a moving image with a large change (motion) of the entire image is input, it is difficult to accurately obtain the flicker amount through the flicker detection unit 80. This is because when the movement of the input image is intense, an increase or decrease in the luminance of the light due to the switching of the image itself occurs in addition to the increase or decrease in the luminance of the light emitted from the liquid crystal display element 50 with the inversion driving of the liquid crystal display element 50 However, it is difficult to distinguish this from flicker.

  For this reason, when an image with a large time change of the histogram is input by analyzing the histogram, it is determined that it is difficult to suppress the occurrence of flicker, and the control selection unit 72 controls the flicker suppression unit 73 to suppress flicker. Do not give instructions. That is, the flicker suppression unit 73 is not allowed to set the flicker suppression driving condition.

  However, even if the input image is a moving image, flicker can be detected if the input image is a moving image with little motion. Whether or not a moving image has a small amount of motion can be estimated from the amount of time change in the histogram. When it is determined that the time change amount of the histogram is small and the flicker amount can be detected, the control selection unit 72 issues a flicker suppression instruction to the flicker suppression unit 73 and sets the flicker suppression drive condition. Let it be done.

  According to the present embodiment, even when a moving image is displayed, occurrence of flicker can be detected with high accuracy, and control for suppressing flicker can be appropriately performed.

  Next, a liquid crystal projector according to a fourth embodiment of the present invention will be described. In the liquid crystal projector of the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

  In the first to third embodiments, the control selection unit 72 issues a flicker suppression instruction to the flicker suppression unit 73 according to the histogram of the input image, and the flicker suppression unit 73 detects the flicker suppression drive condition according to the flicker suppression instruction. The case where (selection) and setting are performed has been described.

  However, the flicker suppression drive condition may be detected by the flicker suppression unit 73 regardless of the presence or absence of the flicker suppression instruction from the control selection unit 72. Then, in response to a flicker suppression instruction from the control selection unit 72, the flicker suppression driving condition that has already been detected and stored by the flicker suppression unit 73 may be set through the drive unit 74.

  Accordingly, when the control selection unit 72 determines that the input image is a flicker-detectable image and changes to an image that is not a flicker-detectable image, flicker suppression driving conditions corresponding to the flicker-detectable image are set. It can be avoided that flicker is not suppressed.

  The flowchart of FIG. 13 shows the flow of flicker suppression processing (control method) performed by the control unit 70 of this embodiment. The flicker suppression process is executed according to a computer program (control program) stored in a memory (not shown) in the control unit 70.

  Step 1 to Step 4 are the same as Step 1 to Step 4 in FIG. 7 described in the first embodiment.

  In parallel with the processing of Step 1 to Step 4, the flicker suppressing unit 73 changes the common electrode voltage (Vcom) until the flicker amount (LVflk) detected through the flicker detector 80 reaches the minimum level (Steps 21, 22, and 23). . Then, the flicker suppression unit 73 stores the common electrode voltage (Vcom) when the flicker amount (LVflk) becomes the minimum level as the flicker suppression driving condition.

  The control selection unit 72 that has determined in step 4 that the input image is a flicker-detectable image issues a flicker suppression instruction to the flicker suppression unit 73. Thereby, the flicker suppressing unit 73 sets the common electrode voltage (Vcom) previously stored as the flicker suppressing driving condition through the driving unit 74.

  On the other hand, the control selection unit 72 that has determined that the input image is not a flicker-detectable image in Step 4 instructs the flicker suppression unit 73 not to set the flicker suppression drive condition (Step 9). The flicker suppression unit 73 that has received this instruction does not set the flicker suppression drive condition.

In the first to fourth embodiments, the case where the control selection unit 72 selects whether or not to set the flicker suppression drive condition or the method for setting the flicker suppression drive condition is changed has been described. Then, whether or not to perform flicker detection by the flicker detector 80 is selected.

  Specifically, when it is determined from the histogram of the input image that the input image is a flicker detectable image, flicker detection by the flicker detector 80 and flicker based on the detection result are the same as in the first to fourth embodiments. Set suppression drive conditions. However, if it is determined that the input image is not a flicker detectable image, the output of the flicker detector 80 is forcibly changed to a predetermined value (a constant value). When the output of the flicker detector 80 is a constant value, the flicker suppression unit 73 cannot detect the flicker amount, and as a result, the flicker suppression drive condition cannot be set.

  According to the present embodiment, as in the first to fourth embodiments, flicker detection and flicker suppression driving conditions can be set with high accuracy, and an inappropriate driving condition based on erroneous flicker detection can be avoided. .

  In the present embodiment, the case where the amplitude of the output of the optical sensor that detects the light from the liquid crystal display element 50 is used as the flicker amount calculation method has been described. However, the inversion driving frequency component of the liquid crystal display element 50 may be extracted from the output waveform of the optical sensor by Fourier transform, and the intensity of the frequency component may be used as the flicker amount (LVflk). Thereby, it is possible to detect flicker with higher accuracy. Further, the output waveform of the optical sensor may be smoothed and the average value may be used as the flicker amount.

  Further, the place where the flicker detector 80 is disposed is not limited to the side of the polarization beam splitter 33c, and may be any place as long as the light from the liquid crystal display element 50 can be detected and the projected light is not blocked. For example, it may be installed inside the projection lens, or may be attached to a light shielding member such as a mask for shielding unnecessary light.

  Further, in the above-described embodiment, as a method for determining whether or not the input image is a flicker detectable image, the case where the mode value is used when specific weighting is performed on the gradation of the histogram has been described. However, other parameters such as the mode value when specific weighting is not applied to the gradation of the histogram, the deviation of the gradation distribution, and the width of the maximum and minimum values of the gradation distribution are used alone or in combination. Also good. Further, it may be determined whether the image is a flicker-detectable image by determining whether it is a moving image or a still image from the time average value of the histogram of several frame images and the amount of change in the histogram.

  Further, when creating a histogram, the input image may not be analyzed as it is, but the input image information may be compressed to create the histogram. As a result, the capacity required for the memory and the time required for processing can be reduced.

  In the above-described embodiment, the case where the applied voltage range is divided into three M, L, and H has been described. However, finer control may be performed by dividing the range into more ranges.

  In addition, the flicker suppression process described in the above embodiment does not always need to be executed, and may be executed at regular time intervals. Alternatively, the input image may be analyzed, and flicker suppression processing may be executed when a large histogram change occurs. The flicker suppression process may be executed when the amount of flicker detected by the flicker detector 80 exceeds a predetermined value.

  Further, as a method for obtaining the flicker suppression driving condition, in the above embodiment, the flicker amount is measured while changing the common electrode voltage of the liquid crystal display element 50, and the common electrode voltage at which the flicker amount becomes the minimum level is determined as the flicker suppression driving condition. As sought. However, the method for obtaining the flicker suppression driving condition may be another method. For example, the flicker suppression driving condition in which the amount of flicker becomes the minimum level by changing the pixel electrode voltage may be obtained.

  Further, the common electrode voltage may be changed from one direction to obtain the common electrode voltage at which the flicker amount becomes the minimum level. In addition, the amount of flicker when two common electrode voltages are set is detected, and an approximate curve equation of the common electrode voltage and the flicker amount obtained in advance is fitted to the two common electrode voltages and the detected flicker amount. Thus, the common electrode voltage as the flicker suppression driving condition may be obtained. By using this method, it is possible to simplify the arithmetic processing for obtaining the common electrode voltage at which the flicker amount becomes the minimum level, and to shorten the time required for the arithmetic operation.

  Further, although the liquid crystal projector has been described in the above embodiment, the present invention can also be applied to other liquid crystal display devices such as a direct-view type liquid crystal monitor using a liquid crystal display element.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  An image display apparatus capable of suppressing flicker with high accuracy can be provided.

DESCRIPTION OF SYMBOLS 1 Liquid crystal projector 50 Liquid crystal display element 70 Control part 71 Input image detection part 72 Control selection part 73 Flicker suppression part 74 Drive part 80 Flicker detector

Claims (4)

A liquid crystal display element for displaying an image by modulating light;
Driving means for driving the liquid crystal display element according to an input image signal;
Flicker detection means for detecting flicker generated in the liquid crystal display element;
Driving condition setting means for setting the driving condition of the liquid crystal display element by the driving means to a specific driving condition for reducing the flicker, using the flicker detection result by the flicker detecting means;
Input image detection means for detecting information relating to the gradation of the input image signal;
In accordance with the information about the gradation, the selection of whether to drive the liquid crystal display element according to the specific driving condition, the selection of whether to detect the flicker by the flicker detection means, and the setting of the driving condition And a selection unit that performs any one of changes in the setting method of the specific drive condition by the unit. The liquid crystal display device according to claim 1, wherein the input image detection unit detects a gradation distribution of the input image as information about the gradation. 2. The liquid crystal according to claim 1, wherein the flicker detection unit includes an optical sensor that detects light from the liquid crystal display element, and detects the flicker by Fourier-transforming an output waveform of the optical sensor. Display device. Liquid crystal display device that modulates light to display an image, drive means for driving the liquid crystal display element in response to an input image signal, and flicker detection means for detecting flicker generated in the liquid crystal display element A control program for controlling a display device,
On the computer,
Setting the driving condition of the liquid crystal display element by the driving means to a specific driving condition for reducing the flicker according to the flicker detection result by the flicker detecting means;
Detecting information relating to the gradation of the input image signal;
In accordance with the information about the gradation, the selection of whether to drive the liquid crystal display element according to the specific driving condition, the selection of whether to detect the flicker by the flicker detection means, and the setting of the driving condition A control program for a liquid crystal display device, comprising: executing a process including a step of performing any one of changes in the setting method of the specific drive condition by means.